Over the past few years, the demand for ever cheaper and lighter weight portable electronic devices has led to a growing need to manufacture durable, lightweight, and low cost electronic circuits including high density memory chips. The increasing complexity of electronic devices, and integrated circuits, coupled with the decreasing size of individual circuit elements, places ever more stringent demands on fabrication processes, particularly with respect to the resolution and accuracy of the fabrication patterns. The ability to fabricate on a nanometer scale guarantees a continuation in miniaturization of functional devices. Micro-fabrication techniques can produce structures having features on the order of nanometers. Micro-fabrication is used in a wide variety of applications, such as the manufacturing of integrated circuits (i.e. semiconductor processing), biotechnology, optical technology, mechanical systems, and micro-electro-mechanical systems (“MEMS”).
Micro-fabrication is typically a multi-step process involving the patterned deposition or removal of material from one or more layers that make up a finished device. Micro-fabrication is sensitive to the presence of contaminant particles. In micro-fabrication it is common to inspect a substrate for the presence of contaminants between process steps. As the size of micro-fabricated features decreases, smaller and smaller contaminant particles and films can affect device yield. A number of tools have been developed for detecting contaminant particles. Inspection tools, such as a scanning electron microscope (SEM) are commonly used to inspect a partially fabricated device or wafer containing multiple devices for defects. For certain cases, it may be sufficient to image the defects, e.g., with the SEM and analyze the image to characterize the defects. But for many cases, once defects have been detected it is important to chemically characterize them
Instrumentation for use in spectroscopy of charged particles for chemical analysis makes use of electrons or ions which are emitted from a substance after being bombarded or irradiated with electrons or ions from a source such as an electron gun. Energy Dispersive X-ray analysis (EDX) is a technique in which an electron beam strikes the surface of a conducting sample. The energy of the beam is typically in the range 5-20 kilo electro-volts (keV). This causes X-rays to be emitted from the point the material. The energy of the X-rays emitted depends on the material under examination. For EDX, the X-rays are generated in a region about 2 microns in depth. For sufficiently large defects, EDX may have adequate sensitivity and spatial resolution. Unfortunately, for very small defects, e.g., less than about 50 nm in size, EDX does not have the sensitivity to chemically characterize them.
Another charged particle spectroscopy technique is known as Auger electron spectroscopy. In this technique, a target sample material is placed in an ultra high vacuum (UHV) environment, typically about 10−10 Torr to 10−9 Torr, and upon being bombarded with electrons from some source, such as an electron gun, the sample gives off a variety of emissions. Among these are X-rays, secondary electrons, and reflected primary electrons from the source. The emissions include Auger electrons (a particular class of secondary electrons) in the manner which is well known in the literature. Auger electron spectroscopy is a surface analytical technique because the energies of the electrons emitted are typically in the range of 50 eV to 3 keV, and at this energy they cannot escape from more than a few nanometers deep in the surface (of course, the higher the energy, the thicker the layer from which they can escape). For Auger spectroscopy to be conducted the sample chamber and spectrometer must be maintained at Ultra High Vacuum (UHV), as any gasses present will form a thin ‘adsorbed gas layer’ on the surface of the sample attenuating the Auger electron signals from the sample. However, the design complexity of UHV systems and slower operational cycle prevents rapid analysis of defects in production-scale substrate processing, which tend to operate at high vacuum, e.g., about 10−7 to about 10−6 torr.
It is within this context that embodiments of the present invention arise.